In a new study, the research team at the Imperial College London has tested the potential of psilocybin-assisted therapy to alleviate treatment-resistant depression. Statistics show that 20% of people suffering from major depression are unresponsive to conventional treatments like SSRI medication or cognitive behavioural therapy (Carhart-Harris et al., 2016).

Twelve subjects (six men and six women), all diagnosed with major depression, participated in the study. They received two oral doses of psilocybin – 10 mg and 25 mg – the former being the safety dose and the latter, administered seven days later, the treatment dose. The participants had been selected among 70 candidates; one of the main selection criteria was the absence of psychotic episodes in subjects themselves and in their immediate family members.

All participants, aged between 30 and 60, had a long history of major depression, with treatment attempts having had only minimal effects. Some of them had been suffering moderate to severe depression for about three decades. Previous treatment attempts included both chemical and psychological means: medication like serotonin or dopamine reuptake inhibitors (SSRI, NDRI, SNRI, etc.) and therapies like cognitive behavioural, group and counselling therapy.

The pharmacology of psilocybin is different from that of selective serotonin reuptake inhibitors (SSRIs), the most common medication for this kind of depression. SSRIs prevent the already released serotonin – one of the neurotransmitters involved in the regulation of emotion – from being taken back up by the same neurons that produced it, so that it can be taken up by serotonin receptors. Unlike SSRIs, psilocybin (converted in the body to psilocin) is structurally similar to serotonin, and causes the same effect as an overall increase in serotonin levels.

Over the course of the study, psychological support was provided before, during and after the psilocybin sessions. During the sessions, there was minimal intrusion into the patients´ experience. The patients were only asked the necessary questions to evaluate the effects of psilocybin on their physical and mental well-being. The most common adverse reactions reported included nausea, headaches, anxiety and confusion, all of which were transient. Only one patient reported transient paranoia that subsided after one hour.

The study demonstrated that the symptoms of depression were somewhat reduced in all of the twelve participants. The scores on the Quick Inventory of Depressive Symptoms (QIDS) showed that the depression level was reduced from 16-20 (severe depression) to 6-10 (mild depression). Five follow-up assessments took place between one week and three months after the treatment. The maximum positive effects were reached two weeks after the treatment. Eight subjects experienced complete remission in their depression one week after the treatment and in seven of them significant reduction in depression persisted after three months. One patient experienced an increase in depressive symptoms during the three months following the treatment.

This study was the first to explore the efficacy of psilocybin in treating major depression, and demonstrated the potential of psilocybin for reducing the symptoms of major treatment-resistant depression and the safety of the substance when administered under proper conditions. Previous research with psilocybin-assisted therapy has already showed that it can alleviate anxiety related to end-stage cancer (Grob C.S. et al., 2011).

Further research in more rigorous conditions (placebo-controlled and on a larger scale) is needed to confirm the potential of psilocybin in treating major depression. If this promise can be fulfilled, it could mean a new chance for millions of people struggling with severe depression.